Shortsightedness or myopia is a common refractive disorder of human eyes. Objects beyond a distance from a myopic person are focused in front of the retina and is perceived as blurry images. Common myopia develops when the eye grows excessively longer than the combined focal length of the optical elements of the eye. Myopia usually progresses in human eyes over time and is typically managed by regularly renewed prescriptions of corrective spectacles and contact lens. Those lenses provide clear vision but do not retard progression of myopia. Undesirable sight-threatening eye diseases are also associated with high myopia. Therefore, there is a need for new technology to reduce the economical and social burden produced by common myopia by providing clear vision and a retardation function at the same time. Recent scientific publications have stated that the dimensional growth of developing eyes is modulated by optical defocus, which is resulted when images are projected away from the retina. Refractive development of the eye is influenced by the equilibrium between defocus of opposite directions. In particular, it has been documented that artificially induced “myopic defocus” (image projected in front of the retina) may retard myopia from progressing further.
U.S. Pat. No. 7,025,460 [Smith] teaches a method to introduce peripheral (off-axis) myopic defocus relative to central (on-axis) focused image to control the progression of myopia. It teaches against projections of defocus on central retina to provide clear vision correction. The method may not be able to achieve optimal effectiveness for retarding myopia progression. A similar problem is evident in the disclosure of PCT application PCT/US2007/070419 [Holden]. Holden teaches that the peripheral optical zone producing defocus be substantially outside the normal pupil diameter of the patient. A similar problem is also evident in the disclosure of U.S. patent application 60/584894 [Phillips]. Phillips suggests a non-concentric design to degrade optical quality.
WO 2006/034652 [To] teaches the use of concentric multi-zone bifocal lenses in which myopic defocus is induced both axially and peripherally for visual objects of all viewing distances. Those teachings have been shown to be effective in both animal study and human clinical trial for retarding myopia progression. However, minor problems have been identified in the clinical trial and is waiting to be improved. The use of bifocal lens taught projects a secondary single homogeneous defocused image, which is sometimes perceived as a bright “ghost” image causing discomfort to the patient. In addition, the homogeneous secondary defocused image might mislead a minor portion of the patients to adjust their accommodation habit and choose to focus with the secondary defocused image instead of the designated primary image and thus jeopardizing the retarding function. Similar problems are evident in U.S. patent application 60/905821 [Phillips], in which a concentric multi-zone bifocal lens using the same principle was described as a form of contact lens.
U.S. Pat. No. 6,045,578 [Collins] discloses a method manipulating spherical aberration for myopia control. In optical and mathematical terms, longitudinal aberration describes the extent where marginal rays are bent more than or less than the paraxial rays. It is different from optical defocus which describes the distance an image is away from the reference image plane (retina in eye). Unlike the case of defocus, it has not gained support from scientific literature and there is no identified report that manipulating spherical aberration has any effect on retarding myopia progression.
U.S. Pat. No. 6,752,499 [Aller] teaches prescribing commercially available bifocal contact lenses to young myopic patients who also exhibit near point esophoria and accommodative lag to control myopia. Its effectiveness is questionable because a higher dose of undesirable hyperopic defocus is induced by the primary refractive power (distant zone) when it teaches to reduce the esophoria and accommodative lag during near vision as it requires the wearer to switch their focus to use the second refractive power (near zone). In addition, it is not supported from more recent literature that esophoria is related to myopia progression.